The present invention relates generally to contact tips (e.g., contact tubes) for gas metal arc welding applications.
A range of welding applications and apparatus are known in the field, typically adapted for a particular type of welding operation. For example, in certain operations commonly referred to as gas metal arc welding (GMAW) or metal inert gas (MIG) welding, a wire is fed from a spool or drum through a welding torch. An electrical charge is placed on the wire via the torch and, as the wire approaches a grounded work piece, an arc is formed. The arc heats the work piece as well as the wire, melting the weld location and adding the wire to the weldment. A shielding gas is applied via the torch that surrounds a progressive weld pool to aid in the formation of the weld and to protect the weld during solidification of the molten metal. Various arrangements and applications exist for wire feed welders. In general, these arrangements and applications function similar to the GMAW and MIG systems described above.
In all GMAW techniques, a persistent problem exists in maintaining good electrical contact between the wire and the charged portions of the torch. That is, the torch typically includes a series of electrically coupled conductive elements that convey charge to the wire as it passes through the torch. One of these elements is a contact tip, the main function of which is to transmit electrical current from the torch to the passing wire. However, because the wire must generally freely pass through the torch as it is driven by a motor and drive mechanism from a spool, less than optimal contact may be made at certain points in the operation. If contact is lost or temporarily interrupted between the contact tip and the wire, a degraded weld may result.
Various arrangements have been devised in attempts to maintain improved contact between the contact tip and welding wire. Certain proposed mechanisms include spring-enhanced contact tips, which tend to be relatively fragile and relatively expensive to manufacture. In addition, other proposed mechanisms include enhanced contacting mechanisms that include several opening slots on the surface of the contact tip. These designs are not practical insofar as welding spatter tends to get into the opening slots and can contaminate the contact tip-to-wire interface. Also, for all of these designs, the friction forces between the contact tip and wire are significantly increased, which can be a big challenge for GMAW on soft wires such as aluminum. There is a need, therefore, for improved techniques for maintaining good electrical contact between the contact tip and the welding wire.